export const imageBase64Resize = (base64, w, callback) => {
	var newImage = new Image();
	var quality = 0.6;    //压缩系数0-1之间
	newImage.src = base64;
	newImage.setAttribute("crossOrigin", 'Anonymous');	//url为外域时需要
	var imgWidth, imgHeight;
	newImage.onload = function () {
		imgWidth = this.width;
		imgHeight = this.height;
		var canvas = document.createElement("canvas");
		var ctx = canvas.getContext("2d");
		if (Math.max(imgWidth, imgHeight) > w) {
			if (imgWidth > imgHeight) {
				canvas.width = w;
				canvas.height = w * imgHeight / imgWidth;
			} else {
				canvas.height = w;
				canvas.width = w * imgWidth / imgHeight;
			}
		} else {
			canvas.width = imgWidth;
			canvas.height = imgHeight;
			quality = 0.6;
		}
		ctx.clearRect(0, 0, canvas.width, canvas.height);
		ctx.drawImage(this, 0, 0, canvas.width, canvas.height);
		var base64 = canvas.toDataURL("image/jpeg", quality); //压缩语句
		// 如想确保图片压缩到自己想要的尺寸,如要求在50-150kb之间，请加以下语句，quality初始值根据情况自定
		// while (base64.length / 1024 > 150) {
		// 	quality -= 0.01;
		// 	base64 = canvas.toDataURL("image/jpeg", quality);
		// }
		// 防止最后一次压缩低于最低尺寸，只要quality递减合理，无需考虑
		// while (base64.length / 1024 < 50) {
		// 	quality += 0.001;
		// 	base64 = canvas.toDataURL("image/jpeg", quality);
		// }
		callback(base64);//必须通过回调函数返回，否则无法及时拿到该值
	}
}

export const base64toFile = (dataurl, filename) => {
	var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
		bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
	while(n--){
		u8arr[n] = bstr.charCodeAt(n);
	}
	return new File([u8arr], filename, {type:mime});
}
